This is a RTD Pt-100 Transmitter, It can Convert Thermocouple mV or RTD mV to 4-20 mA Current. A Mains powered Transmitter not loop powered. The part numbers on Circuit and silk screen may not match. But the PCB may be usable. The output is a current source and not a current sink. It goes to a 4-20mA Mux with a common ground.
Control and Data Acquisition
This low-cost transmitter was made to send RTD information in
a 4-20mA over long distance. The 4-20mA was the input to a
Analog-Mux which interfaced to a PLC system and a 486
The Analog Multiplexer Built around CD4051 was was controlled
by PLC to get data from numerous channels. This reduced the
cost of the System. This is ok when Real-Time Acquisition is
not required. The Analog 4-20 to 4-20 Mux-Buffer circuit can
also be seen at Industrial Process
This was done as customer budget could not afford dedicated analog input modules for every channel. There were more than 50 Inputs. The thermal inertia of system did not need a real time or fast correction.
The job of the transmitter is to take the weak analog measured parameter information from sensor, be close to it, amplify, clean, linearize the signal if required and send strong - error free data over a long distance to an operator or system.
Mux for Data Acquisition
Now with new Technologies like Zigbee and Modbus, We can classify Transmitters as shown below. The Measured Parameter Temperature, Flow or Events Has to reach an Intelligent Data Storage and Analysis System. It may just be an Human Operator who jots the data on a Notepad and Turns a Few Dials based on his Experience or an embedded controller. It could even be a Computer Network or a Web Application used by many, like Monitoring the Weather Attributes.
of Current Loop 4 to 20 mA Standard
You have a three wire RTD, there is also a 4 wire RTD type,
This circuit can be used for both.
In the 3W RTD you have two wires coming from the same point (zero ohms between them) the third wire will be 100 ohms from these two. From the two wires that are at same point take one wire and give 1mA from Q3 + OUT. The other wire of the pair connect to input +..... input - can be connected to the 100E end.
RTD 3-W Mains Powered Temperature 4-20mA Transmitter.
20th Mar 2020
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